This invention relates to a method and apparatus for determining the fusion interface between horizontally disposed batch material and molten glass in a glass melting furnace, and more particularly relates to a method and apparatus for determining the elevation of the fusion interface, wherein an electrical probe is forced downwardly through batch material by cyclically hammering the electrode into the batch and simultaneously continuously downwardly forcing the means for hammering the probe.
It is well known in the electric glass melting art that batch may be supplied to a furnace to form a blanket or cover over all or a portion of a bath of molten glass. A batch blanket or cover is typically formed in vertically oriented electric glass melting furnaces, as is illustrated in U.S. Pat. Nos. 3,583,861 to Preston, 3,524,206 to Boettner et al., 3,852,509 to Rutledge et al., and 3,942,968 to Pieper. As discussed in the Preston patent, the batch cover limits or minimizes heat losses from the molten glass; not only does this lead to conservation of energy, but it also tends to stabilize the convection currents generated in the bath. It will also be appreciated that the furnaces of these patents do not pollute the atmosphere, because there are no flames playing on the batch which will cause dusting or suspension of the particulate and gaseous matter in the air which is withdrawn from above the batch.
The Boettner patent teaches that it is desirable to control the power supply and rate of withdrawal of glass from the furnace to produce a batch cover having a downwardly extending, generally conical or stalactite contour on its lower fusion interface surface with the molten glass. In the Rutledge patent, various problems of maintaining the conical contour of the interface surface are discussed; and electrode arrangements and circuitry which solves the problems are disclosed therein. In brief, the electrodes may be arranged and fired to insure that the central portion of the fusion interface does not dip too deeply to cause unmelted materials to be withdrawn from the furnace and also to insure that the peripheral portions of the fusion interface is properly controlled to prevent both deleterious downward convection currents near the walls and excessive heat losses through the batch near the walls.
In order to control the electrical power supplied to the glass, control circuits, such as disclosed by McQuaid et al. in U.S. Pat. No. 3,636,227, have been suggested. Also, thermocouples have been employed to ascertain temperatures at various locations in the glass to give some indications as to the contour of the fusion interface. However, these devices have not provided the information needed to precisely determine the contour of the batch-molten glass fusion interface.
The present invention provides a method and apparatus for precisely determining the elevation or elevations of the fusion interface between batch and molten glass in an electrically heated glass melting furnace.